1. Field of the Invention
The present invention relates to a solid electrolytic capacitor and to a method of manufacturing cathode material of a cathode for said solid electrolytic capacitor, which comprises: an anode of valve metal or of an alloy of which main component is the valve metal; a dielectric layer formed by anodizing said anode; an electrolyte layer formed on said dielectric layer; and a cathode formed on said electrolyte layer. More particularly, a feature of the invention is to improve cathode material used for a cathode of a solid electrolytic capacitor and to lower equivalent series resistance of the solid electrolytic capacitor.
2. Description of the Related Art
Conventionally, solid electrolytic capacitors have been commonly used for a variety of electrolytic equipments. In recent years, because electrolytic equipments, such as a personal computer having higher frequency have required instant supply of electric power to an electric circuit, a development of a solid electrolytic capacitor wherein equivalent series resistance (ESR) is low at high frequency has been demanded.
It has been proposed to fabricate such a solid electrolytic capacitor by: anodizing an anode of valve metal, such as tantalum, aluminum, niobium and titanium, or of an alloy of which main component is such valve metal, in order to form a dielectric layer of such oxide on the anode surface; overlaying an electrolyte layer comprising, for example, a conductive polymer or manganese dioxide on the dielectric layer; and overlaying a carbon layer and a silver layer as a cathode on the electrolyte layer. (See, for example, Japanese Published Unexamined Patent Application No. 3-46215.)
Examples of factors to cause increase of ESR in the solid electrolytic capacitor include dielectric loss, specific resistance of the electrolyte layer and the cathode, contact resistance between the electrolyte layer and the cathode, and so on. Especially, the specific resistance of the electrolyte layer and the cathode, and the contact resistance between the electrolyte layer and the cathode is a major factor to increase in ESR at high frequency. Therefore, a problem in the solid electrolytic capacitor described above has been that when the specific resistance of the electrolyte layer and the cathode and the contact resistance between the electrolyte layer and the cathode become large, ESR becomes high, especially at high frequency.
In recent years, therefore, a solid electrolytic capacitor comprising a carbon layer containing carbon particles and a benzene compound for decreasing specific resistance of an electrolyte layer and a cathode, and contact resistance between the electrolyte layer and the cathode, has been proposed. (See, for example, Japanese Published Unexamined Patent Application No. 2001-284182.)
Nevertheless, in the above-described solid electrolytic capacitor comprising the carbon layer containing the carbon particles and the benzene compound, it is still impossible to fully improve ESR.